Low power integrated circuits (“ICs”) frequently use groups of circuits or blocks that are enabled and disabled periodically to save power. For example, in a DC/DC power converter operating in a Pulse Frequency Modulation (PFM) mode, circuitry blocks are switched between active and inactive states each clock cycle. In general, these circuitry blocks include digital circuits that are switched on or off, and analog circuits having current sources that also are switched. For high performance analog circuits, requiring fast and stable response, these current sources must be switched on rapidly and settle to a stable value in a short period of time.
Previous attempts to address the issue of quickly enabling a current source have included the use of current steering circuits, which waste current and are not appropriate for low power circuitry. Another solution makes use of a closed-looped circuit, which can degrade the settling time of an output current and in certain cases consume a significant amount of quiescent power. Lastly, another previous solution uses large capacitors, which are area intensive, slow and often sensitive to loading conditions.